Recently, MSEM students from the Marine Resources class collected phytoplankton during their field trip to the Greater Farallones National Marine Sanctuary Visitor Center.  This site, in the shadow of the Golden Gate Bridge, is where seawater enters the San Francisco Bay Estuary and mixes with freshwater coming down from the Delta.  As an oceanographer, Professor Allison Luengen finds this an ideal location to talk about the processes at play in this heavily urbanized estuary.

Two different photos showing several individuals in front of a bridge talking and the other photo showing one individual holding a container of seawater up in front of a bridge.
Left: Professor Allison Luengen (in red jacket) and students collecting plankton.
Right: MSEM student observing a plankton sample.

Phytoplankton are both essential primary producers in this system, and a source of concern.  As primary producers, phytoplankton photosynthesize and are an essential source of food to the marine food chain.  But too much phytoplankton can be a problem!  Some types of phytoplankton produce toxins, creating harmful algal blooms.  Eutrophication, or an increase in the amount of plant growth in the system, can lead to loss of dissolved oxygen.  Conditions that are favorable to phytoplankton growth have been changing rapidly in this estuary, making this an ideal place to study the interaction between nutrients and phytoplankton.

Students collected phytoplankton off of Torpedo Wharf by carefully lowering funnel-shaped mesh nets into the open water and submerging the collection container.  Nets with different mesh sizes were used to capture different sizes of plankton.  Careful collection involved being aware of the current direction and other hazards in the ocean.  Hopefully, a seal does not carry the net away! After 10 minutes, phytoplankton specimens were unscrewed from the cod end of the nets and taken to the nearby Pier Classroom for identification.

A group of people posing for the camera in front of a bridge. One person is holding a fishing net and another is holding the rope.
MSEM students with Prof. Luengen (left) as they prepared to drop collection nets over the Torpedo Wharf fishing pier.

Back at the Pier classroom, students used microscopes to study phytoplankton and zooplankton.  Ecologist Janai Southworth, a volunteer with NOAA, assisted with identification of the phytoplankton species.  A few notable finds were chain-forming diatoms and dinoflagellates, such as Ceratium Noctiluca.  We also saw zooplankton, including copepods and swimming mollusc and barnacle larvae!  Storms in the previous week had mixed some pennate diatoms, which are typically found on the bottom, into the water column, which were a surprising addition to our plankton samples.  Luckily for us, the rain had passed and it was a beautiful day.

Future field trips will be underway this Spring semester – be on the lookout for more with MSEM!

Two photos, one individual looking through a refractometer device in a classroom and the other showing a group of individuals looking through microscopes in a classroom.
Left: An MSEM student in the Pier Classroom used a refractometer to measure salinity at 29 PSU, which is consistent with estuarine mixing.
Right: Students pipetted water samples and looked for species of phytoplankton under the microscopes.